Structural Diversity and Incompatibility Induced Complex Phase Formation Behavior in the Stuffed Tridymites Ca_1–xSr_xGa₂O₄

Abstract

Stuffed tridymites AM 2 O 4 composed of a condensed MO 4 -tetrahedra-based framework have been widely investigated due to their structural diversity and rich physical properties. Herein, the strategy of stuffing mixed Ca 2+ and Sr 2+ cations into the [Ga 2 O 4 ] 2− framework in (Ca 1−x Sr x )Ga 2 O 4 (CSGO, 0 ≤ x ≤ 1) is utilized to manipulate the phase formation behavior with different structure types at particular annealing temperatures. Five derivatives, including αand β-CaGa 2 O 4 , βand γ-SrGa 2 O 4 , and new CSGO-type structures, were observed. The distinctive feature of the CSGO-structure is the coexistence of UUDDUD-and UDUDUD-type six-membered rings, where U (up) and D (down) denote the orientations of GaO 4 -tetrahedra with respect to the plane grids, in a ratio of 2:1. Single-phase α-Ca 1−x Sr x Ga 2 O 4 (x < 0.2) and γ-Ca 1−x Sr x Ga 2 O 4 (x > 0.67) could be obtained at low temperatures. Biphasic regions, including α-Ca 1−x Sr x Ga 2 O 4 /CSGO (0.2 ≤ x ≤ 0.67), γ-Ca 1−x Sr x Ga 2 O 4 /CSGO (0.67 < x ≤ 0.8), and β-Ca 1−x Sr x Ga 2 O 4 /CSGO (0.8 < x < 1), were observed at the intermediate temperature region and evolve irreversibly into the CSGO single-phase region upon elevating the temperature. Moreover, the structure−property relationship of the new CSGO-phase was further studied by doping coordinationsensitive Bi 3+ activators to advance the development and applications of stuffed tridymites.

Boosted Activity of Cobalt Catalysts for Ammonia Synthesis with BaAl2O4–xHy Electrides

“…Such a 3D network structure without non-bridging oxygens leads to robustness toward air and moisture. Furthermore, there are cage-like void spaces with diameters of 5–6 Å surrounded by Ba 2+ ions in the lattice (Figure b) . Such crystallographic voids are suitable for the stabilization of anionic electrons .…”

“…Furthermore, there are cage-like void spaces with diameters of 5−6 Å surrounded by Ba 2+ ions in the lattice (Figure 1b). 18 Such crystallographic voids are suitable for the stabilization of anionic electrons. 9 If the lattice O 2− sites can be replaced by H − ions, then electrons are expected to be accommodated in the interstitial cage sites (Figure 1b), as shown in eq 1, to preserve the charge balance because neither Ba 2+ nor Al 3+ has other oxidation states.…”

Exclusive confinement of Bi3+-activators in the triangular prism enabling efficient and thermally stable green emission in the tridymite-type phosphor CaBaGa4O8:Bi3+

“…Herein, we shift our attention to a family of Bi 3+ -activated tridymite-type gallates AGa 2 O 4 (A = Ba 2+ , Sr 2+ , Ca 2+ ), where the structural symmetry strongly depends on the A-cation size, as presented in Table 1. [25][26][27][28][29] The structural diversity of these gallates generates various coordinating environments for the A-sites, which is suitable for the accommodation of Bi 3+ ions, thereby leading to tunable emission wavelengths for AGa 2 O 4 : Bi 3+ phosphors. For instance, Lin et al reported that Ba 1+x Sr 1−x Ga 4 O 8 :Bi 3+ phosphors exhibit extremely broadband spectra, covering the spectral range from purple-blue to deep red (350-900 nm).…”